Dennis O'Mann and his doll watch the St. Patrick's Day Parade in New York. Photograph: Carlo Allegri/Reuters

The Sydney Opera House goes green as part of a global initiative by Tourism Ireland which also sees the Pyramids of Giza, the Christ the Redeemer statue in Rio de Janeiro, the London Eye, Selfridges in London, Niagara Falls, the Prince's Palace of Monaco, Burj al Arab in Dubai and the Leaning Tower of Pisa, turn a shade of green this weekend. Photograph: Jean-Pierre Bratanoff-Firgoff

Tourists in Dublin for the St Patrick's festival look at a map outside the Tourist office on Suffolk Street. Photograph: Brenda Fitzsimons/The Irish Times

Renowned Dublin historian Pat Liddy photographed on South William Street guiding a tour of Dublin in celebration of St Patrick. Photograph: Brenda Fitzsimons /The Irish Times

Kimberly Anderson wears an "Irish Princess" necklace as she watches the St Patrick's Day Parade in New York. Photograph: Carlo Allegri/Reuters

James Hennessy, aka 'St Patrick', with a nine-foot adult American Alligator at the Reptile Village, Gowran, Co Kilkenny, as preparations for St Patrick's Day continue in Dublin and around the world. Photograph: Julien Behal/PA Wire

Members of FDNY march on New York's Fifth Avenue during the 252nd annual St Patrick's Day Parade. Photograph: Ramin Talaie/Getty Images

Workers dye the Chicago River green to kick off the city's St Patrick's Day celebration in Illinois. The dyeing of the river has been a tradition in the city for 43 years. Photograph: Scott Olson/Getty Images

Aras an Uachtarain illuminated green for the first time this year for St Patrick's Festival. Photograph: Peter Moloney/OPW Ireland

The EDF London Eye is lit green by Tourism Ireland to celebrate St Patrick's Day in London. Photograph: David Parry/PA Wire

Visitors from Australia join the peoples parade ahead of the St Patricks Day Parade during festivities on Dublins O'Connell Street. Photograph: Alan Betson/The Irish Times

Babon Njiel from Gambia; Kamil and Meg Borawscy from Poland; and Howard Davis and Mark Harrison from Yorkshire get in to the spirit of St Patricks Day on O'Connell Street, Dublin. Photograph: Alan Betson/The Irish Times

St Patricks Day festivities at the start of the Festival Parade on O'Connell Street. Photograph: Alan Betson/The Irish Times